Prosthetic devices, such as stents or grafts, may be implanted during interventional procedures such as balloon angioplasty to reduce the incidence of vessel restenosis. To improve device effectiveness, implantable medical devices may be coated with one or more therapeutic agents providing a mode of localized drug delivery. The therapeutic agents are typically intended to limit or prevent restenosis. For example, anti-thrombogenic agents such as heparin or clotting cascade IIb/IIIa inhibitors (e.g., abciximab and eptifibatide) may be coated on the stent, thereby diminishing thrombus formation. Such agents may effectively limit clot formation at or near the implanted device. Some anti-thrombogenic agents, however, may not be effective against intimal hyperplasia. Therefore, the implantable medical device may also be coated with anti-proliferative agents or other compounds to reduce excessive endothelial re-growth. Therapeutic agents provided as coating layers on implantable medical devices may effectively limit restenosis and reduce the need for repeated treatments. Therapeutic agents that provide other benefits, such as anti-plaque agents, e.g., naproxen and ibuprofen, also be may desirably coated onto an implantable medical device.
Several strategies have been developed for coating one or more therapeutic agents onto the surface of an implantable medical devices. Standard methods may include dip coating, spray coating, and chemical bonding. The therapeutic agent coating may be applied as a mixture, solution, or suspension of polymeric material and/or drugs dispersed in an organic vehicle or a solution or partial solution. However, the creation of an implantable medical device coating such that a drug may be delivered in a reliable but controlled manner presents many challenges, particularly the need to dissolve the drug inside the polymer carrier. Such drug dissolution often requires the use of solvents to dissolve the drug, and further solvents or co-solvents to dissolve the polymer. As such, finding the right solvents with the right polymer to deliver the right drug can be difficult to achieve. What is needed is a drug-eluting polymeric coating for an implantable medical device that does not require the use of co-solvents between the drug and the polymer carrier.
Hydrophilic polymeric coatings containing antibiotic zeolites known in the art may provide one solution to this problem. The antibiotic zeolites are created by an ion-exchange process wherein antibiotic metal ions; such as, silver, copper or zinc ions, are retained on zeolite particles through an ion exchange reaction. The antibiotic zeolites are dispersed in a hydrophilic polymer, for example, by high shear mixing, and the hydrophilic polymer is then dissolved in an organic solvent to provide a coating solution for a medical article. Such an antibiotic hydrophilic polymer coating is disclosed in U.S. Pat. No. 6,436,422 to Trogolo et al., which is incorporated by reference herein in its entirety. However, a need still exists for a drug-eluting polymeric coating for an implantable medical device with a controlled dosing profile that can be used to deliver a greater variety of therapeutic agents and that does not require the use of co-solvents between the therapeutic agent and the polymer carrier.